Specifications

Page 12 Remote Procedure Call Programming Guide

The relevant routine is svc_getargs() which takes an SVCXPRT handle, the XDR routine, and a pointer to

where the input is to be placed as arguments.

3.2. Memory Allocation with XDR

XDR routines not only do input and output, they also do memory allocation. This is why the second

parameter of xdr_array() is a pointer to an array, rather than the array itself. If it is NULL, then xdr_array()

allocates space for the array and returns a pointer to it, putting the size of the array in the third argument.

As an example, consider the following XDR routine xdr_chararr1() which deals with a ﬁxed array of bytes

with length SIZE.

xdr_chararr1(xdrsp, chararr)

XDR *xdrsp;

char chararr[];

{

char *p;

int len;

p = chararr;

len = SIZE;

return (xdr_bytes(xdrsp, &p, &len, SIZE));

}

If space has already been allocated in chararr, it can be called from a server like this:

char chararr[SIZE];

svc_getargs(transp, xdr_chararr1, chararr);

If you want XDR to do the allocation, you would have to rewrite this routine in the following way:

xdr_chararr2(xdrsp, chararrp)

XDR *xdrsp;

char **chararrp;

{

int len;

len = SIZE;

return (xdr_bytes(xdrsp, charrarrp, &len, SIZE));

}

Then the RPC call might look like this:

char *arrptr;

arrptr = NULL;

svc_getargs(transp, xdr_chararr2, &arrptr);

* Use the result here

svc_freeargs(transp, xdr_chararr2, &arrptr);

Note that, after being used, the character array can be freed with svc_freeargs() svc_freeargs() will not

attempt to free any memory if the variable indicating it is NULL. For example, in the the routine

xdr_ﬁnalexample(), given earlier, if ﬁnalp->string was NULL, then it would not be freed. The same is true

for ﬁnalp->simplep.

To summarize, each XDR routine is responsible for serializing, deserializing, and freeing memory. When

an XDR routine is called from callrpc() the serializing part is used. When called from svc_getargs() the

deserializer is used. And when called from svc_freeargs() the memory deallocator is used. When building